The overall objective of this proposal is to investigate the regulation of nitrogenase, nitrate reductase, and nitrite reductase in relation to the ammonia utilizing enzymes glutamine synthetase, glutamate synthase, and glutamate dehydrogenase in blue-green algae. This involves experiments to determine the levels of these varied enzymes in cells grown with different nitrogen sources. These, and similar experiments, are designed to provide information about the regulatory patterns of these enzymes. In addition to the growth studies, regulation will be examined by isolating mutants having altered activities and/or control of these enzymes. Growth inhibitory analogs such as methionine sulfoximine and methylamine will be used to isolate resistant mutants. Auxotrophs for ammonia, glutamine, and glutamate will be isolated. These strains will be characterized as to enzyme presence and activity with a view toward genetic analysis in the future.